Selenium cycle

Evidence for a selenium cycle is found through the study of selenium accumulator plants. These plants are found in semi-arid, seleniferous soils. The plants biosynthesize forms of organic selenium compounds and release the compounds into the soil when they decay. If the compounds were not oxidized, then an increase in organic selenium would be seen, but selenium in these areas is mainly inorganic.^[2]

Aquatic ecosystems

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Related topics Biogeochemistry geochemical cycle chemical cycling environmental chemistry Biosequestration Deep biosphere Ocean acidification acid rain Biogeochemical planetary boundaries
Research groups DAAC GEOTRACES IMBER NOBM SOLAS
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v t e

There are three fates of dissolved selenium in an aquatic ecosystem: 1. it can be absorbed or ingested by organisms; 2. it can bind with suspended solids or sediments; or 3. it can remain in free solution.^[3] Over time, most of the selenium is taken in by organisms or bound to other solids. As the suspended material settles, the selenium accumulates in the top layer of sediment. Due to the dynamic flow in an aquatic ecosystem, selenium is usually only in the sediments temporarily before being cycled back into the system.

Immobilization processes

Selenium can be removed from the ecosystem and bound in sediment through natural processes of chemical and microbial reduction of the selenate form to the selenite form. The reduction is followed by

Mobilization processes

Selenium is made available to the food chain through four oxidation and methylation processes. The first process is oxidation and methylation of inorganic and organic selenium by plant roots and microorganisms.^[3] The second process is biological mixing and associated oxidation of sediments from the burrowing of benthic invertebrates and feeding of fish and wildlife. The third process is represented by physical movement and chemical oxidation from water circulation and mixing, such as current, wind, precipitation, and upwelling. The fourth process is from oxidation by plant photosynthesis.^[4]

References